Exercise is extremely important, as it stimulates appetite and builds muscle. Although the American and Australian show methods seem to be very different, this is what we do:
Steers - penned for day, let out in individual runs every night. The size needs to be big enough to stimulate appetite and build muscle, without them walking condition off. I have heard from various people, but it seems half to one acre is about right for each animal. Also, all steers let out together in a paddock one day a week for interaction and playing.
Heifers, cows and bulls - as above but not penned during day. Free to move from run to shedded pen as they wish.